1. Field of the Invention
This invention relates to cooling of rollers. More especially, but not exclusively, the invention concerns the cooling of rollers used for transporting a continuously cast strand of partially and wholly solidified metal from an open-ended mould positioned to receive molten metal from a tundish.
2. Discussion of the Prior Art
One of the developments that has taken place in steel making over the past years has been continuous casting of liquid steel. In this process liquid steel is poured continuously from a tundish into an open-ended mould and is continuously extracted therefrom as a partially solidified strand by a train of rollers. The process is such that the outer skin of the steel solidifies sufficiently within the confines of the mould to enable the continuous strand of cast steel to be extracted therefrom and transported by the rollers along a curved downwardly inclined path while containing, at least initially, still liquid metal in the inside of the strand.
It will be appreciated that this process imposes considerable heat stresses upon the rollers which are at any given time in contact with the steel strand and where the rollers are internally cooled, usually by water circulating within them, considerable attention has to be paid to the cooling process to avoid asymmetric heating during thermal cycling of the rollers during both normal and abnormal casting conditions. The usual arrangement of water cooling within such a roller is through bores which extend between the roller ends with the axis of each bore set at the same distance from the roller surface. The number of bores provided is usually as high as possible and the bores are conventionally positioned as near to the surface of the roller as possible while retaining the necessary strength to sustain geometric stability and minimise bending of the roller during both normal and abnormal casting conditions.
A disadvantage which arises with such known rollers occurs at the roller ends where the flow of liquid passing towards one roller end through one peripheral bore must be returned along another peripheral bore to the opposite end of the roller; also, inlets and outlets must be provided to admit liquid to and to remove liquid from the roller. This problem is complicated by the fact that the roller is conventionally produced from a solid piece of machined metal, through which it is only possible to drill straight bores. This has meant that the flow of fluid through the bores does not continue to the bore ends but is diverted along angled bores remote from the bore ends to provide zig zag connecting paths between the communicating peripheral bores. It will be appreciated that such an arrangement means that the ends of the roller are not cooled to the same extent as the remaining length of the roller; consequently, particularly severe overheating during plant stoppage or thermal cycling can take place especially with centre bearing rollers. Also, the multiplicity of angled bores required places a limit on the number of peripheral bores which can be present without adversely affecting the geometric stability of the rollers during normal and abnormal casting conditions.
Because of the need to machine into a conventional internally cooled roller a multiplicity of angled bores, the production costs of such rollers is high. Rollers in accordance with the present invention, however, can be produced relatively cheaply because inter alia the number of angled bores is significantly reduced.